1. Field of the Invention
The present invention relates to a motor for an electrical system, and more particularly to a motor which can be driven by a low or high voltage supplier without providing an additional apparatus such as a transformer.
2. Description of Prior Arts
Generally, electrical apparatuses are divided into two groups, that is, those which can be driven by an alternating current supplier and the others which can be driven by a direct current supplier. The other is a cordless type vacuum cleaner wherein a battery which is provided therein and produces a direct current at a low voltage when compared to that of the wire type vacuum cleaner, is used as a current supplier without using the alternating current supplier. In a conventional wire type vacuum cleaner, a universal motor which can be driven by a direct or an alternating current supplier is used. In the meantime, the cordless vacuum cleaner uses a small motor which is driven by a direct current supplier.
FIG. 1 is a schematic diagram for illustrating a universal motor used in a conventional electrical apparatus. As shown in FIG. 1 a commutator 103 is secured to the lower portion of a shaft 102 of an armature 101. Two brushes 104a and 104b are provided on both sides of commutator 103 so as to come in contact with commutator 103. The ends of two stator coil groups 105a and 105b which are wound on stators (not shown) are connected to brushes 104a and 104b, respectively. Further, two electrical source nodes P1 and P2 are connected to the other ends of stator coil groups 105a and 105b, respectively.
FIG. 2 is a schematic diagram showing a group of armature coil 101 which is wound on pieces of commutator 103 and in slots formed on the core surface portion of armature 101 in a conventional motor as shown in FIG. 1. As shown in FIG. 2, armature coil 101a is wound between on twenty two slots of armature 101 and on twenty-two commutator pieces according to a double winding back alpha method. Here, double winding is referred to a method of winding a coil wherein armature coil 101a is inserted in a single slot and wound on armature 101 in both directions along the longitudinal direction of armature 101 so that armature coil 101a forms a closed circuit. Back alpha is referred to winding type wherein armature coil 101a is connected to a hook of a commutator piece. More particularly with reference to FIG. 2, armature coil 101a which is connected to a commutator piece a1 in an alpha type, is wound through slots 1 and 12 of armature 101 in a longitudinal direction thereof by a predetermined number of turnings and then connected to a commutator piece a2 in an alpha type. Armature coil 101a is wound through slots 2 and 13 of armature 101 by the same number of turnings. In the same manner, armature coil 101a is further wound through each slot and finally amateur coil 101a is wound from slot 22 to slot 11 and connected to commutator a11 so that the entire armature coil 101 forms a closed circuit. At each slot of armature 101, two armature coils are wound in the opposite directions by the same number of turnings.
In the meantime, the number of turnings of armature coil 101a determines the power of the motor.
With reference to FIG. 3, an operation of the conventional motor will be explained. At first, when a plus current source is applied to node P1, a current passes through stator coil 105a and brush 104a. Then, the current is applied to armature coil 101a through the hook of the commutator pieces and passes through stator coil 105 of the other side and flows to a current node P2.
Accordingly, the shaft of the stator comes to have an N pole and a P pole in accordance with the direction of the current to produce a magnetic field. Due to the relation between the current direction of armature coil 101a (inserted in the slot of the armature core 101) and the polarity of the shaft, a rotation power is produced according to Fleming's left hand rule. Thus, armature 101 starts to rotate. If the amateur rotates, the contact portions between commutator 103 as a rotator and brushes 104a and 104b as a stator changes continuously so that the current supplying point to armature coil 101a is continuously shifted in accordance with the formation of the slots of the armature core. However, the current direction is not changed independently of the shift of the current supplying point, the armature continues to rotate in a predetermined direction during the supply of the current.
Here, the rotating direction is determined by the winding direction of stator coils 105a and 105b or the connection between armature 101 and commutator 103. In a conventional universal motor as above, the rotating direction remains unchanged although an alternating current source is applied instead of the direct current source. That is, when the alternating current is applied so that the current direction is changed, the magnetic field direction formed by the stator coil is also changed according to the current direction change. Therefore, the rotating direction of the armature is unchanged. Due to this fact, the universal motor can be driven either by a direct current source or by an alternating current source.
Generally, the alternating current source which is publicly used is a high voltage source such as 110 V or 220 V (there is a difference according to an individual nation). However, a unit cell constituting a battery for producing a direct current can not provide a voltage more than 2 V. Therefore, batteries wherein a plurality of unit cells are connected in series for providing a low voltage such as 12 V, 24 V, 48 V etc. are commercially available.
Therefore, in order to obtain a voltage as high as the public alternating current by using only the battery, a plurality of batteries should be connected in series. In such a case, the number of the batteries and the weight of the power source should be increased proportionally. In a small electrical apparatus such as a conventional vacuum cleaner, there must be a limitation in view of the size and the weight thereof. Therefore, the vacuum cleaner should be divided into one wherein an alternating current source is used and the other wherein a direct current source is used. That is, in a vacuum cleaner wherein the alternating current source is used, a motor having an appropriate coil for the high voltage alternating current source is used so as to produce a desired power. In the meantime, in a vacuum cleaner wherein a battery is used as an electrical power source, a cord for an alternating current power source is not used and a motor producing a desired power at a low voltage is used so that the size and the weight of the battery may be reduced. Accordingly, in a conventional vacuum cleaner for household appliance, one wherein a motor for only a public high voltage is provided is used when a public high voltage is used at home, and another wherein a motor only for a low direct voltage from a small number of batteries is used when a motor for battery is used as an electrical power source. Therefore, in a small electrical apparatus such as a vacuum cleaner, either a high voltage or a low voltage should be used as a power source and producing an electrical apparatus wherein both a high voltage source such as the public alternating power source and a low voltage source such as a battery may be used alternatingly was impossible.